fix: use the appropriate ID when trying to import github_team_members objects

[brandon-at-wrk]

When importing a github_team_member, the import command passes in the data as the
"Id", not the "team_id", causing the import step to fail when parsing an empty string
as a number. Should fix #608, as I hit the same error.

[brandon-at-wrk]

I tested this by following these notes and running terraform import github_team_members.team_members <ID>. I do not know how to unit test this, since it seems like the current tests ought to have caught it.

[SpencerMalone]

Good catch! I actually had also just dug in and realized this was the problem. The generic error actually had me all tripped up in thinking it was the schema validation at first. I think that old issue from 2020 is something else, but this definitely solves a very active problem in the recent release.

My only Q (and this comes from a place of ignorance w/ the codebase):

Do we need to repeat the pattern from resource_github_team_membership.go of...

	// We intentionally set these early to allow reconciliation
	// from an upstream bug which emptied team_id in state
	// See https://github.com/integrations/terraform-provider-github/issues/323
	d.Set("team_id", teamIdString)
	d.Set("username", username)

@ https://github.com/integrations/terraform-provider-github/blob/main/github/resource_github_team_membership.go#L85-L99 ?

[brandon-at-wrk]

I believe line 85 using the split on d.Id() makes it safe in this case, since it seems like the id in import x <id> is set as the value of d.Id() -- I haven't tested that import case, so I cannot be sure.

[SpencerMalone]

@kfcampbell any chance this could get bumped up in priority? It effectively makes the newest resource added unusable until this is merged. If there's another individual or group you'd like tagged, lemme know!

[brandon-at-wrk]

For anyone blocked by this, you can take the patch, follow these steps, and run the imports. Since this only breaks imports, the rest of your workflow can remain the same after your import step.

[kfcampbell]

Thank you for the contribution! I'll get this released shortly.